Studies have been conducted in conscious dogs to evaluate the hemodynamic, renal and electrophysiologic effects of a variety of agents possessing potential cardiac effects. To date, studies have been conducted with the following agents: Pentazocine, Hydroxyzine, Ajmaline, Nicotine, Procaine amide and Lidocaine. Initial studies with pentazocine have demonstrated potential antiarrhythmic effects. Hemodynamic effects included an increase in heart rate as well as a rise in aortic pressure and systemic resistance. Studies with hydroxyzine, a tranquilizer with potential antiarrhythmic effects demonstrated minimal antiarrhythmic and hemodynamic effects. This would suggest that its mode of action may be via central or peripheral nervous system effects. Studies with ajmaline, a rauwolfia alkaloid with potent antiarrhythmic effects, have demonstrated selective depression of intra-ventricular conduction associated with temporary increase in aortic pressure and peripheral resistance. Studies with nicotine have demonstrated that this alkaloid: (1) releases acetylcholine in the right atirum; (2) may depress myocardial function; and (3) produces hypertension and a reflex bradycardia. Finally, studies with procaine amide and lidocaine have shown that: (1) these agents have minimal hemodynamic effects in therapeutic dosage and (2) procaine amide depresses intra-ventricular conduction and renal blood flow. Studies are continuing with: (1) chronic infusion of these drugs; and (2) dogs with acute myocardial infarction to further elucidate the pharmacologic effects of these and other cardiac drugs.